A conventional cylindrical lock shown in FIGS. 1 and 2 comprises an U-shaped shackle 10, a cylindrical housing 12 and a lock member 17. For locking it, a leg 11 of the shackle 10 is inserted in an oval-shaped hole 120 in the housing 12, letting a curved-in notch 110 of the leg 11 engage a projection 14 of the end of the cylindrical housing 12 and an end of another leg 15 insert in a round hole 121 of the housing 12. Then a key 16 is used to rotate the lock member 17, making a projecting block 18 also rotate to move up a stop plate 19 so as to engage a slot 150 in the end of the leg 15, and consequently the shackle 10 is locked immovable, impossible to be pulled out of the housing 12.
If this lock in position is to be unlocked, i.e. to free the shackle 12 from the housing 12, a key 16 has to rotate the lock member 17, moving the stop plate 19 down to the original position, and the shackle 10 is to be pushed to incline to the left, disengaging the curved-in notch 110 from the projection 14 and then the shackle 10 can be pulled out of the housing 12.
This conventional cylindrical lock has been found to have drawbacks listed below.
1. In locking process, the shackle has to be inserted inclinedly in the housing in order to engage the curved-in notch 110 of the shackle 12 with the projection 14 of the cylinder 12.
2. The key has to be used to rotate the lock member so as to move down the stop plate 19 for the leg 15 of the shackle 10 to insert in the hole 121 of the housing 12.
3. The U-shaped shackle has to be inserted in the holes of the housing 12 in a precise position that the leg 11 is at the left side and the leg 15 is at the right side, otherwise it can not be locked, because the notch 110 and the slot 150 in the two leg ends have different forms and direction.
4. The stop plate only locks one leg 15 of the shackle 10, so this lock has not excellent anti-burglary safety.
5. In unlocking, the shackle 10 has to be inclined to a large angle, so this conventional lock has a restriction for places where it is used.